Digging for the Trough about Navicular Syndrome
2nd part
When we discuss the pathology behind navicular disease, we must understand that the real problem lies in the fact that most domestic horses are incapable of landing on their heels in soft footing and surely not in the rocky terrain they were born to roam. When a horse is sensitive on rocky terrain, most people blame the soles, but watch closely how they move. Almost every time they will shorten their stride, landing on their toes, and lean forward. They are keeping their sensitive frogs and underlying digital cushions out of harms way. Dr. Bowker has established that the longer they try to move this way, the weaker the structures become.
Continued toe first landing stresses and tears the attachment of the impar ligament (the attachment of P3 and navicular bone). The navicular bone is a part of the articulating surface of the joint between P2 and P3. When the horse lands on its toes, the weight of the horse then slams back into the navicular bone as the heels rock down. This constantly tears away at the impar ligament. 80% of the blood supply to the navicular bone goes through the impar ligament. Bowker blames a loss of circulation through the impar ligament for many of the navicular bone changes, as well as the attempts to repair this attachment leaving ossifications on P3 and the navicular bone.
Michigan State University has also found that the bone loss often diagnosed as navicular disease is the result of a lack of natural pressure (think of the bone loss suffered by astronauts during extended stays in space) in the region from continued toe first landing, and Dr. Bowker is consistently finding much more damage to the coffin bone in navicular horses, with 40-60% bone loss in P3 being common. Specifically he blames peripheral loading, or loading the walls only without the aid of natural sole support and toe first landings. Either situation robs P3 of the natural pressure it requires to maintain health and function.
